The invention concerns a method for the reduction of the image steadiness error in the projection of films, which consist of individual images, in accordance with the preamble to claim 1, an apparatus for the measurement of the image position in accordance with the preamble to claim 13, and a device for the correction of an image steadiness error in accordance with the preamble to claim 20.
When making a film, the film in the camera is moved step by step past the screen window for the exposure.
After the development and the production of a copy, which is conventionally produced in the contact exposure process, the film strip is available with its sequence of individual images. For reproduction by means of a projector, the film strip is moved step by step past the projection lens, whereby because of the rapid succession of the projection of the phase images, physiologically the impression of a continous movement process is caused.
The transport step is realized by mechanical step switch mechanisms (Maltese cross/projector, gripper drive/camera) or also by step motors or controlled direct current drives.
The attainable precision of the step size of the camera drive, of the reproduction drive and the division of the film strip define the image steadiness which is to be achieved. If the image steadiness is unsatisfactory, the next image will not be as exactly projected on the same position of the screen as the previous image. This error is described as the image steadiness error.
A reduction of the image steadiness error below the range which is visible to the observer or even only an approximation to this order of magnitude is yet not possible, to this day.
The camera producers of film cameras attempt to minimize the image steadiness errors caused by the camera. The same applies to the producers of film projectors. The exactnesses of the film strip are defined in a corresponding norm.
Everything is done on the premise of keeping the partial errors below 0.1% and from the aspect that the errors of the others are predetermined. The partial errors are time offset, position offset and are dependent on different apparatus, users and methods, and therefore they cannot be influenced. Even if one's own partial errors, which can only be influenced from this point of view, can be reduced to zero, there remains a theoretical residual error of 0.2%. But in practice, the largest share of errors is due to the projector.
As a further complication, there is the fact that it is necessary to make all the methods compatible with the immense quantities of film material which are available today on the market and which arrive day by day. It makes no sense to deprive these films of their economic usefulness by special solutions.
A method, as decribed in the introductory part of claims 1, 13 and 18 is disclosed in DE 39344 20 C2. For measuring the steadiness of image sensors are provided, and a compensation of deviations is provided by generating error tables and by an adaptive empirical control of the drive motor.
In the U.S. Pat. No. 5,175,580 a photo camera is disclosed which provides an optical compensation of vibrations at free hand photography, i.e. an image stabilisation.